fix: 修正学习流程中的证据、复习与进度问题

- 独立尝试按课程要求校验内容，不再任意输入即算独立成功
- 复习节点改为学后第 1/3/7/14 天，之后每 30 天抽查；复习轮换情境
- 掌握状态按作答记录推导：需认识、可回忆、跨情境使用及最近两次无帮助
- 课程证据按实际用到的目标记录；跟读与课程对话只算辅助练习
- 复习成功不再降低已有状态
- 学完课程后进入下一节未完成课程；全部学完后引导巩固与阶段评估
- 新增 3 题基础定位，按结果设置起始课程
- 新增按课程开放的对话场景，首页推荐最少练习的场景
- 切换课程时清空上一课的步骤进度
- AI 返回 JSON 格式并按 JSON 回放历史；拼写校验忽略大小写与连字符；移除学习目标选择

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

kouyu_english/lib/core/seed_courses.dart

@@ -1116,7 +1116,16 @@ bool matchesSegmentIndependent(String segmentId, String response) {
       .expand((segments) => segments)
       .where((item) => item.id == segmentId)
       .firstOrNull;
-  if (segment == null) return true;
+  if (segment == null) {
+    // Single-segment lessons: every group of the lesson's independent task
+    // has to be present. Unknown segments never pass.
+    final lessonId = segmentId.replaceFirst(RegExp(r'-[a-z]$'), '');
+    final groups = a0IndependentRequiredTerms[lessonId];
+    if (groups == null) return false;
+    return groups.every(
+      (group) => group.any((term) => _containsTerm(text, term)),
+    );
+  }
   if (segmentId == 'a0-04-a' || segmentId == 'a0-04-b') {
     final count = segment.independentRequiredTerms
         .where((term) => text.contains(_normalizeDialogueInput(term)))
@@ -1129,10 +1138,64 @@ bool matchesSegmentIndependent(String segmentId, String response) {
             .length >=
         3;
   }
-  return segment.independentRequiredTerms
-      .any((term) => text.contains(_normalizeDialogueInput(term)));
+  return segment.independentRequiredTerms.any(
+    (term) => text.contains(_normalizeDialogueInput(term)),
+  );
 }
 
+const _introductionTerms = [
+  "i'm + #word",
+  'i am + #word',
+  'my name is',
+  "my name's",
+];
+
+/// What the independent attempt of each single-segment lesson has to contain.
+/// Each inner list is one part of the task; a part passes when any of its
+/// terms appears. Terms follow the same syntax as [LessonDialogue.requiredTerms].
+const a0IndependentRequiredTerms = <String, List<List<String>>>{
+  // 介绍你的名字并回应 Nice to meet you
+  'a0-01': [
+    _introductionTerms,
+    ['nice to meet you'],
+  ],
+  // 介绍名字并拼读它
+  'a0-02': [
+    _introductionTerms,
+    ['#spelling'],
+  ],
+  // 问候并说出你的状态
+  'a0-03': [
+    ['hello', 'hi', 'hey', 'how are you'],
+    ['good', 'okay', 'ok', 'fine', 'great', 'tired'],
+  ],
+  // 说出一个身边物品
+  'a0-05': [
+    ["it's a", 'it is a', "it's an", 'it is an'],
+  ],
+  // 说来自哪里并反问对方
+  'a0-06': [
+    ["i'm from", 'i am from'],
+    ['where are you from', '#question'],
+  ],
+  // 介绍一位家人或朋友
+  'a0-07': [
+    ['this is my'],
+  ],
+  // 说一个喜好并反问
+  'a0-09': [
+    ['i like', 'i love'],
+    ['do you like', '#question'],
+  ],
+  // 完成姓名、地点、喜好和反问
+  'a0-10': [
+    _introductionTerms,
+    ["i'm from", 'i am from', 'from + #word'],
+    ['i like', 'i love'],
+    ['#question'],
+  ],
+};
+
 class LessonDialogue {
   const LessonDialogue({
     required this.goal,
@@ -1172,8 +1235,17 @@ bool _containsTerm(String text, String term) {
 }
 
 bool _matchesStructure(String text, String token) => switch (token) {
-  // Three or more letters said one by one, e.g. "S-H-E-N" or "s h e n".
-  '#spelling' => RegExp(r'(?:^|[^a-z])[a-z](?:[ -][a-z]){2,}').hasMatch(text),
+  // Letters said one by one ("S-H-E-N", "s h e n", "L-I"), or the spelled
+  // name typed as one word ("Shen", "aaa"). Case and hyphens are ignored.
+  '#spelling' =>
+    RegExp(
+          r'(?:^|[^a-z])[a-z](?:\s*[-\u2010-\u2015]\s*[a-z]|\s[a-z])+(?![a-z])',
+        ).hasMatch(text) ||
+        RegExp(r'^[a-z]{2,}$').hasMatch(
+          text
+              .replaceAll(RegExp(r'[-\u2010-\u2015]'), '')
+              .replaceAll(RegExp(r'^[^a-z]+|[^a-z]+$'), ''),
+        ),
   // Any spoken or written digit.
   '#digit' => RegExp(
     r'(?<![a-z])(zero|one|two|three|four|five|six|seven|eight|nine|ten)(?![a-z])|[0-9]',
@@ -1232,21 +1304,150 @@ const a0MeetDialogue = LessonDialogue(
   requiredTerms: [
     ["i'm + #word", 'i am + #word', 'my name is', "my name's", 'name is'],
     ["i'm from", 'i am from', 'from + #word'],
-    [
-      'good',
-      'okay',
-      'ok',
-      'fine',
-      'great',
-      'tired',
-      'i like',
-      'i love',
-    ],
+    ['good', 'okay', 'ok', 'fine', 'great', 'tired', 'i like', 'i love'],
     ['#question'],
   ],
   taskLabels: ['介绍姓名', '说明来自哪里', '表达状态或喜好', '反问对方'],
 );
 
+/// A free practice scene. It opens once [unlockAfterLessonId] is complete
+/// (always open when null) and only uses language taught up to that lesson.
+class DialogueScene {
+  const DialogueScene({
+    required this.id,
+    required this.title,
+    required this.summary,
+    required this.script,
+    required this.recapPrompt,
+    this.unlockAfterLessonId,
+  });
+
+  final String id;
+  final String title;
+  final String summary;
+  final LessonDialogue script;
+
+  /// The follow-up review prompt added after the scene is finished.
+  final String recapPrompt;
+  final String? unlockAfterLessonId;
+}
+
+const a0Scenes = [
+  DialogueScene(
+    id: 'a0-meet',
+    title: '初次见面',
+    summary: '介绍姓名、地点、状态或喜好，并反问对方',
+    script: a0MeetDialogue,
+    recapPrompt: '再用英语介绍一次自己。',
+  ),
+  DialogueScene(
+    id: 'a0-number',
+    title: '留个电话',
+    summary: '问候、报出号码、再说一遍，并反问对方',
+    unlockAfterLessonId: 'a0-04',
+    recapPrompt: '用英语报一次你的虚拟电话号码。',
+    script: LessonDialogue(
+      goal: '问候并交换一个虚拟电话号码',
+      prompts: [
+        'Hi! How are you today?',
+        'Good. What\u2019s your phone number? Use a fake number.',
+        'Sorry, please say it again.',
+        'Thanks! Now ask me one question.',
+      ],
+      hints: [
+        'I\u2019m good, thanks.',
+        'My number is one-three-eight.',
+        'One-three-eight.',
+        'What\u2019s your phone number?',
+      ],
+      translations: [
+        '嗨！你今天好吗？',
+        '好的。你的电话号码是多少？用一个虚拟号码。',
+        '抱歉，请再说一遍。',
+        '谢谢！现在问我一个问题。',
+      ],
+      requiredTerms: [
+        ['good', 'okay', 'ok', 'fine', 'great', 'tired'],
+        ['#digit'],
+        ['#digit'],
+        ['#question'],
+      ],
+      taskLabels: ['说出你今天的状态', '报出一个号码', '再说一次号码', '反问对方'],
+    ),
+  ),
+  DialogueScene(
+    id: 'a0-photo',
+    title: '看照片聊天',
+    summary: '介绍照片里的人和东西，说喜好，并反问对方',
+    unlockAfterLessonId: 'a0-07',
+    recapPrompt: '用英语介绍一位家人或朋友。',
+    script: LessonDialogue(
+      goal: '介绍照片里的人和物品',
+      prompts: [
+        'Nice photo! Who is this?',
+        'And what\u2019s this in the photo?',
+        'Where are you from?',
+        'Cool! Now ask me one question.',
+      ],
+      hints: [
+        'This is my sister.',
+        'It\u2019s a bag.',
+        'I\u2019m from Hong Kong.',
+        'Who is this? / What\u2019s this?',
+      ],
+      translations: ['照片真好！这是谁？', '照片里这个是什么？', '你来自哪里？', '真酷！现在问我一个问题。'],
+      requiredTerms: [
+        ['this is my', 'this is'],
+        ["it's a", 'it is a', "it's an", 'it is an'],
+        ["i'm from", 'i am from', 'from + #word'],
+        ['#question'],
+      ],
+      taskLabels: ['介绍照片里的人', '说出照片里的物品', '说出你来自哪里', '反问对方'],
+    ),
+  ),
+  DialogueScene(
+    id: 'a0-plan',
+    title: '约个时间',
+    summary: '说星期和整点，回答喜好，并反问对方',
+    unlockAfterLessonId: 'a0-09',
+    recapPrompt: '用英语说今天星期几和现在几点。',
+    script: LessonDialogue(
+      goal: '说明星期、时间和喜好',
+      prompts: [
+        'Hi! What day is it today?',
+        'What time is it now?',
+        'Do you like coffee or tea?',
+        'Me too! Now ask me one question.',
+      ],
+      hints: [
+        'It\u2019s Friday.',
+        'It\u2019s three o\u2019clock.',
+        'I like tea.',
+        'Do you like music?',
+      ],
+      translations: ['嗨！今天星期几？', '现在几点？', '你喜欢咖啡还是茶？', '我也是！现在问我一个问题。'],
+      requiredTerms: [
+        [
+          'monday',
+          'tuesday',
+          'wednesday',
+          'thursday',
+          'friday',
+          'saturday',
+          'sunday',
+        ],
+        ["o'clock", 'oclock', "it's + #digit", 'it is + #digit'],
+        ['i like', 'i love', 'yes', 'no', "i don't"],
+        ['#question'],
+      ],
+      taskLabels: ['说出今天星期几', '说出现在几点', '说出你的喜好', '反问对方'],
+    ),
+  ),
+];
+
+DialogueScene sceneById(String id) =>
+    a0Scenes.where((scene) => scene.id == id).firstOrNull ?? a0Scenes.first;
+
 const a0Dialogues = <String, LessonDialogue>{
   'a0-01': LessonDialogue(
     goal: '问候、介绍姓名并回应见面问候',
@@ -1341,7 +1542,12 @@ const a0Dialogues = <String, LessonDialogue>{
       ['my number is + #digit', "my number's + #digit", 'number is + #digit'],
       ['yes', 'no', "that's right", 'right', 'correct'],
       ['#digit'],
-      ["what's your phone number", 'what is your phone number', 'your phone number', 'your number'],
+      [
+        "what's your phone number",
+        'what is your phone number',
+        'your phone number',
+        'your number',
+      ],
     ],
     taskLabels: ['报出一个三位号码', '确认或纠正听到的号码', '再说一次这三个数字', '反问对方的号码'],
   ),
@@ -1422,7 +1628,12 @@ const a0Dialogues = <String, LessonDialogue>{
       ['who is this', "who's this"],
       ['this is my', 'this is'],
     ],
-    taskLabels: ['介绍一位家人或朋友', '完整说出 This is my … 句型', '反问 Who is this', '再介绍一个人'],
+    taskLabels: [
+      '介绍一位家人或朋友',
+      '完整说出 This is my … 句型',
+      '反问 Who is this',
+      '再介绍一个人',
+    ],
   ),
   'a0-08': LessonDialogue(
     goal: '说明星期或整点',
@@ -1440,7 +1651,15 @@ const a0Dialogues = <String, LessonDialogue>{
     ],
     translations: ['今天星期几？', '现在几点了？', '请说一个完整的时间句子。', '现在请问我今天是星期几！'],
     requiredTerms: [
-      ['monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday', 'sunday'],
+      [
+        'monday',
+        'tuesday',
+        'wednesday',
+        'thursday',
+        'friday',
+        'saturday',
+        'sunday',
+      ],
       ["o'clock", 'oclock', "#digit + o'clock"],
       ["it's + o'clock", "it is + o'clock", "it's + #digit", 'it is + #digit'],
       ['what day is it', 'what day', '#question'],
@@ -1488,7 +1707,13 @@ const a0Dialogues = <String, LessonDialogue>{
     requiredTerms: [
       ['say that again', 'again', 'pardon'],
       ['slowly', 'slow'],
-      ["what's your name", 'what is your name', 'where are you from', 'your name', '#question'],
+      [
+        "what's your name",
+        'what is your name',
+        'where are you from',
+        'your name',
+        '#question',
+      ],
       ['i like', 'i love'],
     ],
     taskLabels: ['请求对方重复', '请求对方放慢语速', '反问名字或来自哪里', '说出一件你喜欢的事物'],